1. Field of the Invention
This invention relates to the refining of glyceride oils in the food industry. More particularly, this invention is directed to the removal of free fatty acids and soapstock from oils during refining.
2. Description of the Prior Art
Unrefined glyceride oils contain undesirable minor components or impurities such as pigments, free fatty acids, phospholipids and oxidation products which, unless removed, render the oil commercially unsuitable in that they produce undesirable color or an xe2x80x9coffxe2x80x9d flavor. Further, higher melting components such as wax are undesirable and must be removed from glyceride oils if they are to be used in food products such as salad oil as such components xe2x80x9ccrystalizexe2x80x9d and separate from the rest of the oil when refrigerated. Such unrefined oils are generally refined by one or several of the following steps: degumming, neutralizing or alkali refining to reduce the fatty acid content thereof, bleaching, dewaxing and deodorization. To bleach, the neutralized oil is typically heated in the presence of bleaching clay, such as Fuller""s earth, a naturally porous aluminum silicate. The oil is then subjected to a separation process after which it may be further polished and processed. The spent Fuller""s earth contains from 15-50 percent by weight glyceride oil. This can account for a loss of 2% of the oil stream and can result in a waste product which is environmentally unfriendly.
In refining of glyceride oils, such as vegetable oils, free fatty acids are neutralized through an alkali process. Such neutralization is typically performed through the addition of a 10-15% sodium hydroxide solution to the crude oil, which also acts to hydrate gums or lecithin also present. In neutralizing the free fatty acids, xe2x80x9csoapstockxe2x80x9d is formed from the free fatty acids. This soapstock, or xe2x80x9cheavy phase,xe2x80x9d must be removed from the oil as it will otherwise inactivate bleaching clay and further deteriorates the oil during the deodorizing step. Removal is typically performed by continuous centrifugation. Phospholipids, after treatment with alkali, precipitate out with the soapstock. Sometimes the refining stage is carried out in two steps, as in the case of soybean oil processing where first the gums are separated by hydration and centrifuged and then the oil is neutralized with caustic solution and removed by centrifuging. Other alkali solutions, such as sodium bicarbonate, calcium hydroxide, potassium hydroxide, magnesium hydroxide, ammonia, and some organic bases are known in the art of alkali refining of a crude glyceride oil. There is a need for an alternative to caustic refining, such as a physical refining where oil impurities are removed by physical means. There is also a need for a separation technique of increased economic efficiency as compared to centrifugation.
Centrifugation operations are usually more expensive than other physical separation techniques, produce more oil loss and sometimes require the use of a water wash. A water wash becomes necessary when saponified free fatty acids, or soap, become entrained in the oil. Under these conditions, the centrifuged oil is washed with hot water in an amount up to 15% of the oil weight. The use of extra water requires an additional centrifuging step for removal and creates a waste product that is considered a pollutant and thus is not readily disposable.
It is an object of the invention to provide a process of refining glyceride oil wherein the undesirable components are removed from the crude glyceride oil.
It is a further object to provide a process whereby a non-caustic treatment is used to neutralize impurities in crude glyceride oil.
It is a further object of the invention to create at least a two-phase system to facilitate separation of impurities from the glyceride oil.
It is yet another object to separate a discrete phase from a liquid phase based upon physical characteristics of each phase.
It is yet a further object of the invention to provide an economic alternative to centrifugation as a method of separating impurities from the glyceride oil.
It is yet a further object of the invention to remove impurities from glyceride oil through filtration.
The present invention includes a method and apparatus for removal of soapstock from oils during refining through the use of a liquid refining agent that causes the soapstock to agglomerate allowing for physical separation. The method of the current invention of refining glyceride oil to remove contaminants includes contacting the glyceride oil with an agglomeration agent, causing the contaminants to agglomerate, and physically separating the agglomerated contaminants from the glyceride oil. Glyceride oils or glycerides are found in vegetable oils, such as soybean oil, corn oil, linseed oil, olive oil and peanut oil, and in animal fats, such as lard, tallow, and butter. There are monoglycerides, in which only one OH group of glycerol has been esterified, and diglycerides and triglycerides. Triglycerides are transformed by the human body to release energy or to be deposited as fat. Triglycerides are thus a desirable component of food oils.
Of the many types of glyceride oils derived from vegetables, rice bran oil is unique in that it contains oryzanol. Oryzanol, a valuable nutrient, is destroyed by caustic treatment. The current invention preserves the oryzanol content of the refined oil product. Soybean oil is also notable due to the large volume produced worldwide.
The contaminants that are most often encountered in crude oils and that are agglomerated by the method of the current invention include free fatty acids, waxes, metal ions, phospholipids, pigments or oxidation products.
The agglomeration agent in a preferred embodiment is a soluble silicate solution, the concentration of soluble silicate solution being effective to form a discrete phase and liquid phase, the liquid phase containing the oil. When contacting the agglomeration agent with the oil, the oil preferably has a temperature maintained above 150xc2x0 F. (xcx9c66xc2x0 C.). More specifically, maintaining the temperature between 170xc2x0 F. (xcx9c77xc2x0 C.) and 200xc2x0 F. (xcx9c93xc2x0 C. ) is preferred.
The concentration of soluble silicate is from at least fifteen (15) percent by weight in the soluble silicate solution up to the solubility limit. A preferred percentage is at least 30%. A preferred form of soluble silicate in the solution is sodium silicate with a weight ratio of silicon dioxide to sodium oxide is less than about 3.3, and preferably between 0.91 to 3.3.
Physical separation is performed by filtration. Optionally, a filter aid may be employed to facilitate filtration. Examples of such filter aids include diatomaceous earth and Fuller""s earth, among others.
An embodiment of the method of the invention includes the addition of a bleaching agent that functions to bleach and facilitate filtration. The bleaching agent is introduced in one of several ways including addition during refining or contact through pre-coating on a filter. Certain substances act as both a filter aid as well as interacting in the bleaching/deodorizing process.
The present invention includes an apparatus for refining crude glyceride oil to remove contaminants including a refining vessel for receiving the crude glyceride oil and an agglomeration agent, the agglomeration agent causing the contaminants to agglomerate within the refining vessel. Separation means is also provided to physically separate the agglomerated contaminants from the glyceride oil. A preferred embodiment also includes bleaching means that effects the contact of the glyceride oil to a bleaching agent such that a bleach-treated glyceride oil is physically separated from the agglomerated contaminants. The bleaching means may be incorporated into the separation means. The apparatus may also contain deodorizing means.
The product produced with the method of the invention is a refined glyceride oil from crude glyceride oil refined through contact with an agglomeration agent that acts to reduce soap content to no more than 80 parts per million.
The method and apparatus of the present invention as well as other features, advantages, benefits and objects thereof over other methods and apparati known in the art may be better understood with reference to the detailed description which follows in conjunction with the drawings.